Environmental sensor network

ABSTRACT

A environmental sensor network having at least two environmental sensor units and a central display unit. Each sensor unit includes a sensor adapted to measure a condition and a transmitter adapted to operate in an “activation” mode in which the transmitter transmits a predefined sequence and a sensor ID and a “data” mode in which the transmitter transmits data based on the measurement. The central display unit includes a receiver adapted to receive a transmission from the two environmental sensors, a memory device, and a processor adapted to selectively operate in an “add” mode in which the processor records the presence of an environment sensor unit in the memory device upon the receipt of the predefined sequence and the sensor ID, and a “display” mode in which the processor outputs information based on the measurement.

CROSS-REFERENCE TO RELATED APPLICATIONS

This application is a continuation of prior application Ser. No.10/347771, filed 19 Jan. 2003, which is incorporated in its entirety bythis reference.

BACKGROUND

Moisture meters exist today in various forms. There are complex moisturemeters used by agriculture and gardening professionals as part of alarger weather monitoring or irrigation system. In the case of weathermonitoring systems, they generally are used to record soil moisturealong with a collection of other weather related data to detect trendsto aid in making decisions affecting crop yield. Moisture meters aresometimes part of largescale irrigation systems used with golf coursesor other large properties for the purpose of water management. Theselarge systems are sometimes moveable, but still too large and expensiveto be suitable for household use.

Handheld moisture meters, which are suitable for household use, exist aswell, however, these are standalone devices without the ability to benetworked to a common display unit. This limits their functionalitysince the user must be in the same physical location as the soil to bemeasured. Moreover, if there are multiple locations, with different soiltypes or different watering patterns, the user must go to each locationto take the moisture reading.

Most recreational gardeners employ an “appearance and feel” technique todetermine if their plants require watering. In other words, theyvisually examine the soil and feel it to see whether or not it is damp.This technique is used because is it simple and does not require specialequipment. The disadvantages are that it is time-consuming and requiresspecialized knowledge in order to obtain an accurate reading. It is alsodifficult to estimate the moisture level at soil substantially below thesurface.

SUMMARY

The invention consists of portable handheld sensors wirelessly networkedto a common display unit. This makes it possible for the user to observethe moisture level of the soil in multiple locations from a singleconveniently positioned display unit. The goal is to keep the soilmoisture below the saturation level and above the permanent wiltingpoint. This window is referred to as the management allowed depletion(MAD) zone. Saturated soil lacks the necessary oxygen and dry soilcauses plant stress. Soil kept within the MAD zone, however, is a goodenvironment for healthy plants.

In one aspect, the invention relates to a wireless soil moisture meternetwork. The wireless network includes a plurality of handheld sensorunits and a portable central display unit. Each of the handheld sensorunits includes a sensing probe to measure moisture content in soil, anda wireless transmitter to transmit the measurement through a wirelesschannel. The portable central display unit receives and displays themeasurement from the sensor units.

Embodiments of the above aspect of the invention may include one or moreof the following features. The sensing probe includes a tube filled witha porous material, e.g., gypsum. Each of the sensor units also includesa synch button which, when pressed, enables the transmitter to send abit sequence indicating the presence of the sensor unit. Each of thesensor units may also include a temperature sensor to measure soiltemperature.

The central display unit may include a channel selector. The centraldisplay unit may also include a mode selector, which may be used toselect a first, second, third, fourth, fifth, or sixth mode. The firstmode toggles between display of a single sensor unit's measurement andsimultaneous display of measurements from multiple sensor units. Thesecond mode toggles between a numerical value and a non-numericaldescriptor describing a moisture level. The third mode permits a sensorunit to be added to the wireless network. The fourth mode permits asensor unit to be deleted from the wireless network. The fifth modecauses all of the sensor units to be deleted from the wireless network.The sixth mode causes an alarm to sound when the measured moisturecontent is below a predetermined threshold.

In another aspect, the invention relates to a method of establishing awireless soil moisture meter network. The method comprises (a) using aportable central display unit to assign a wireless channel number to aremote sensor; (b) placing the central display unit in a wait stateuntil a predefined bit sequence is received; and (c) enabling the sensorto send the predefined bit sequence and a unique identifier of thesensor to the central display unit.

Embodiments of the above aspect of the invention may include one or moreof the following features. The method may include repeating the steps of(a), (b), and (c) to add additional remote sensors to the network. Themethod may also include storing the identifier at the central displayunit for the assigned channel number. The central display unit may beset to an ADD mode before the wireless channel number is assigned. Thewireless channel number may be assigned using a channel button of thecentral display unit. The central display unit enters the wait statewhen a synch option is selected at the central display unit. Thepredefined bit sequence may be sent when a synch button is activated atthe remote sensor.

Embodiments may have one or more of the following advantages. The sensorunits and the central display unit are all portable, making the networkquick and easy to set up. Once established, the network provides aconvenient way to monitor the moisture level of the soil in variouslocations. The low cost of the network makes it suitable for householduse. It is simple to add more sensors to the network, so the network canbe scaled up to accommodate lawns, gardens, and potted plants of varioussizes.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 shows an example of a wireless soil moisture meter network;

FIG. 2 shows a remote sensor unit (RSU) in the network;

FIG. 3 shows a central display unit (CDU) in the network;

FIG. 4 illustrates a process of the CDU for reading the measurementsfrom the RSUs;

FIG. 5 shows a Liquid Crystal Display (LCD) and a user interface of theCDU; and

FIG. 6 shows a process of the CDU for adding a channel to the network.

DETAILED DESCRIPTION

FIG. 1 shows a wireless soil moisture meter network lo including aplurality of remote sensor units (RSU) 11 and 12, and a central displayunit (CDU) 15. Each of the RSUs includes a probe 116 or 126 that isplaced in the soil to read the moisture content, a converter unit 118 or128 to convert the sensor reading into a digital value, and a wirelesstransmitter 110 or 120 that sends signals representing the digital valueto the CDU 15. The CDU 15 receives the signals from the plurality ofRSUs 11 and 12 and displays the readings on an LCD screen 18. The CDU 15also includes a user interface 16 that allows the user to select theformat of the readings.

FIG. 2 shows an embodiment of the RSU 11. The RSU 11 is handheld andhighly portable so that the RSU can be easily relocated. The RSU 11 issuitable for indoor or outdoor use. The RSU 11 has a plastic casing 21.The plastic casing 21 of RSUs intended for outdoor use is weatherproofand includes a rubber seal. The plastic casing 21 prevents water anddust from interfering with the interior electronics. The RSU 11 has itsown power source, which may be a battery housed inside the plasticcasing 21 or a solar array 28 affixed to the top of the RSU.

The probe 116 of the RSU 11 includes a metal rod 22 enclosed by anon-corrodible metal tube 23, e.g., stainless steel or aluminum. Insidethe tube 23 is a porous material 24 such as gypsum. Numerous holes 25are drilled into the tube 23 so that moisture may pass through the holesbetween the gypsum 24 and the soil to be measured. The user may leavethe RSU 11 in contact with the soil. However, the user may replace theRSU 11 approximately every two years since the porous material 24 insidethe tube 23 dissolves over time.

The tube 23 is inserted into the soil within the root zone of interest.Water in the soil naturally moves in and out of the gypsum 24, dependingon the level of soil moisture. The fluctuating moisture level in thegypsum 14 causes changes in the gypsum's electrical characteristicsincluding conductivity. Higher moisture levels cause an increase in theconductivity. These conductivity changes are then measured with avoltmeter 26 to produce an analog voltage measurement.

When a measurement is taken, a fixed amount of current is sent throughthe metal rod 22. Then the voltage between the rod 22 and the tube 23 ismeasured with voltmeter 26. This voltage divided by the currentrepresents the resistance of the gypsum 24. The resistance levelindicates the moisture content in the gypsum 24.

In an alternative embodiment, the probe 116 may include two metallicrods or plates enclosed by a nonmetallic tube. The rods may take theform of two traces etched into a circuit board. Operation is similar tothe embodiment in FIG. 2 except that the voltmeter 26 is connected tothe two rods to measure the resistance between them.

The voltage measured in the probe 116 is applied to an analog to digitalconverter (ADC) 27 to produce a digital data stream. The ADC 27 may be aspecialized component, a 555 timer circuit, or a microcontroller with ananalog input. In the case of a 555 timer circuit, the timer circuitgenerates a stream of square wave pulses. The duration of each pulse isa function of the voltage applied to the circuit. The varying durationof the pulses is interpreted in the RSU 11 or by a microcontroller inthe CDU 15.

The RSU 11 generally takes measurements on a relatively infrequent basis(e.g., every half hour) to conserve power. The frequency of themeasurements may be a fixed frequency or may be set by the user. Eachnew measurement may be triggered by either a digital timer or a slowlydraining capacitor in the RSU 11.

The RSU 11 may also possess the ability to measure the temperature ofthe soil. A thermistor or a solid-state temperature sensor may beembedded in a plastic tip 20 of the probe 116. In the case of thethermistor, the voltmeter 26 may be used to measure the thermistor'sresistance, which varies with temperature. This resistance measurementis sent to the ADC 27 where a digital temperature value is produced.Alternatively, the solid-state temperature sensor produces a digitaltemperature value directly. In both cases, the digital temperature valueis combined with the moisture measurement and sent to the transmitter110 for transmission to the CDU 15.

Before sending the digital data stream to the CDU 15, the wirelesstransmitter 110 modulates the carrier frequency with the data stream.The data stream consists of a header (a sequence of bits preprogrammedin the RSU 11 and CDU 15), a sensor ID code, and a most recent moisturemeasurement. Since the transmissions are short in duration relative tothe frequency of the measurements, all of the RSUs 11 and 12 use thesame frequency. This is effectively a time-division multiple accesssystem, but the RSUs 11 and 12 themselves are not synchronized. The RSUs11 and 12 simply transmit whenever a new reading is taken. In the caseof a digital timer, a randomizer may be employed to slightly delay thetransmission to reduce the chance of two RSUs repeatedly transmitting atthe same time.

The user may use a synch button 29 on the RSU 11 to override the normaltransmission cycle for the purpose of testing or adding a new RSU to thenetwork lo. When the synch button 29 is pressed, the transmitter 110immediately sends a special bit sequence indicating the presence of thenew sensor as well as the sensor's unique ID. For testing, the RSU 11also takes a moisture measurement upon pressing the synch button 29 andsends the measurement to the CDU 15.

FIG. 3 shows an embodiment of the CDU 15. The CDU 15 is a separate unitthat receives the measurements from the RSUs 11 and 12 through anantenna 34 and displays the readings from the RSUs on the LCD screen 18.The CDU 15 is approximately 4″×6″×0.25″ and is therefore very portable.The CDU 15 is powered by a power source 33, which may be batteriesreplaceable by the user. When the power is low, a “low battery”indicator appears on the LCD screen 18. The CDU 15 can also be used toverify proper installation of the RSUs 11 and 12. Immediately afteradding a RSU to the network 10 and inserting the RSU into the soil, theuser may press the synch button 29 on the RSU and observe themeasurement on the LCD screen 18 to verify proper installation. The CDU15 also includes a receiver 31, a microcontroller (MCU) 32, and the userinterface 16. The receiver 31 and MCU 32 may be implemented on separateintegrated circuits.

FIG. 4 illustrates a process 40 of the receiver 31 and the MCU 32 forreading the measurements from the RSUs. The MCU 32 is initially in asleep mode. When the receiver 31 detects a known bit sequence (box 41),the receiver wakes up the MCU 32 (box 42). The receiver 31 does notdistinguish between the various RSUs, instead the receiver demodulatesthe incoming signal and passes the resulting data stream to the MCU 32(box 43).

The MCU 32 compares the data stream from the receiver 31 against the IDsof the various RSUs stored in registers inside the MCU 32 (box 44). Whenthe incoming data stream matches one of the IDs, the pulse pattern thatfollows is stored for processing. The pulse stream is compared against alookup table to determine the corresponding moisture reading (box 45).The moisture reading is then stored as the latest value in the registerfor the channel corresponding to that RSU (box 46). The values from allthe RSUs are stored within the CDU 15 so that any channel may beexamined by the user at any time.

The user may view the moisture measurements on the LCD screen 18. In theexample shown in FIG. 5, at the top of the screen 18 is a labelindicating the mode that the CDU 15 is currently in. The CDU 15 may beset to one of the modes: ALL (display all), NUM (numerical display), ADD(add a channel), DEL (delete a channel), CLR (clear all channels), andBUZ (activate the alarm). On the left side of the screen 18 is a channellabel 52 indicating the channel to which an RSU is assigned. To theright of the channel label 52 is the latest measurement 53 from the RSUcorresponding to that particular channel. At the bottom of the screen 18is a message line 54 that helps the user understand the various modes ofthe CDU 15.

In FIG. 5, the user interface 16 consists of three buttons. One buttonis a CHANNEL button 55. Pressing the CHANNEL button 55 allows the userto cycle through the various channels to observe the reading from thedesired RSU. The second button is a MODE button 56. By pressing thisbutton 56, the user can cycle through the six modes of the CDU 15. Thethird button is a SELECT button 57, which is used to choose optionswithin each of the CDU modes.

One of the CDU modes is the ALL (display all) mode, which allows theuser to view the moisture measurements on multiple channelssimultaneously. In one possible implementation, nine channels may bedisplayed on the LCD screen 18 at the same time. In the event that thereare more than nine channels, the measurements may be shown in groups ofnine. The CHANNEL button 55 may be used to cycle through the variousgroups. The mode is activated by pressing the MODE button 56 until theword “ALL” is displayed at the top of screen 18. The message line 54will say “ONE/ALL”. When the user presses the SELECT button 57, all or agroup of the active channels are displayed simultaneously and themessage line 54 changes to “ONE/ALL”. To return to the single channelformat, the user presses the SELECT button 57 again.

The user may choose between numerical and non-numerical formats of themeasurements displayed on the LCD screen 18. The non-numerical formatmay include icons describing moisture levels graphically. For example,the icon can be a glass containing a variable amount of water. Thenon-numerical format may include descriptors such as DRY, DRY+, REG,WET, or WET+. To select a particular display format, the user pressesthe MODE button 56 until the word “NUM” is displayed at the top of thescreen 18. The message line 54 then says “WORD/NUM”. When the userpresses the SELECT button 57, the measurements are displayed innumerical form (e.g., a numerical scale from 1 to 10) instead of wordform and the message line 54 changes to “WORD/NUM”. To return to thenon-numerical format, the user presses the SELECT button 57 again.

As shown by an example in FIG. 6, the user may add a RSU to the network10 by following a multi-step add procedure 60:

-   -   1. The user presses the mode button 56 until ADD is displayed at        the top of the screen 18 (box 61).    -   2. The user selects the channel by pressing the channel button        until the desired channel is shown on the left side of the        screen 18 (box 62).    -   3. The message line displays the word “Synch” which prompts the        user to press the SELECT button 57 to initiate a synch process.        The CDU 15 is put into a WAIT state such that it is expecting a        predefined bit pattern (indicating the. presence of a new        sensor) from a new RSU (box 63).    -   4. Then the user presses the synch button 29 on the new RSU (box        64). This causes the new RSU to transmit the predefined bit        pattern as well as its unique ID to the CDU 15 (box 65).    -   5. The CDU 15 stores the new ID into a register corresponding to        the selected channel. The message line indicates to the user        that the new ID has been received and the sensor was added to        the network (box 66).

The user may also delete a channel from the network 10 by following amulti-step delete procedure:

-   -   1. The user presses the MODE button 56 until DEL is displayed at        the top of the screen 18.    -   2. The user presses the CHANNEL button 55 until the channel to        be deleted is shown on the left side of the screen 18.    -   3. The user presses the SELECT button 57 to delete the channel        shown. The message line 54 indicates the channel has been        successfully deleted.

Rather than delete each channel individually, the user has the option ofdeleting all of the channels at the same time. The mode is activated bypressing the MODE button 56 until the word “CLR” is displayed at the topof the LCD screen 18. The message line 54 then says “Clear all?”. Whenthe user presses the SELECT button 57, all of the active channels aredeleted and the message line 54 changes to “Done”.

The user also has the option to activate an alarm to sound if one of theRSUs is reporting a low level of soil moisture. The alarm is triggeredwhen the moisture reading is below a predefined threshold. In somescenarios, this threshold may be changed by the user. For example, theuser may set a different threshold for different plant types. This modeis activated by pressing the MODE button 56 until the word “BUZ” isdisplayed at the top of the LCD screen 18. The message line 54 then says“Alarm ON/OFF”. When the user presses the SELECT button 57, the alarmfunction is activated and the message line 54 changes to “Alarm ON/OFF”.If any of the RSUs reports a “DRY+” measurement for a predefinedextended period, the alarm sounds periodically until a REG, WET, or WET+reading is reported. A special alarm icon may also appear on the LCDscreen 18 to warn the user of the dry soil condition.

Accordingly, other embodiments are within the scope of the followingclaims.

1. An environmental sensor network comprising: a first environmentalsensor unit including a sensor adapted to measure a condition and atransmitter adapted to operate in an “activation” mode in which thetransmitter transmits a predefined sequence and a first sensor ID and a“data” mode in which the transmitter transmits data based on themeasurement; a second environmental sensor unit including a sensoradapted to measure a condition and a transmitter adapted to operate inan “activation” mode in which the transmitter transmits a predefinedsequence and a second sensor ID and a “data” mode in which thetransmitter transmits data based on the measurement; and a centraldisplay unit including a receiver adapted to receive a transmission fromthe first environmental sensor and to receive a transmission from thesecond environmental sensor, a memory device, and a processor adapted toselectively operate in an “add” mode in which the processor records thepresence of the first environment sensor unit in the memory device uponthe receipt of the predefined sequence and the first sensor ID andrecords the presence of the second environment sensor unit in the memorydevice upon the receipt of the predefined sequence and the second sensorID, and a “display” mode in which the processor outputs informationbased on the measurement.
 2. The environmental sensor network of claim1, wherein the sensors of the first environmental sensor unit and thesecond environment sensor unit are adapted to measure the relativeamount of a particular element or compound in a substance.
 3. Theenvironmental sensor network of claim 2, wherein the sensors of thefirst environmental sensor unit and the second environment sensor unitare adapted to measure the relative amount of water in the substance. 4.The environmental sensor network of claim 2, wherein the sensors of thefirst environmental sensor unit and the second environment sensor unitare adapted to measure the relative amount of the particular element orcompound in soil.
 5. The environmental sensor network of claim 2,wherein the sensors of the first environmental sensor unit and thesecond environment sensor unit are adapted to measure the relativeamount of water in soil.
 6. The environmental sensor network of claim 1,wherein the sensors of the first environmental sensor unit and thesecond environment sensor unit are adapted to measure temperature. 7.The environmental sensor network of claim 1, wherein the sensors of thefirst environmental sensor unit and the second environment sensor unitare adapted to measure an electrical characteristic.
 8. Theenvironmental sensor network of claim 7, wherein the sensors of thefirst environmental sensor unit and the second environment sensor unitare adapted to measure voltage.
 9. The environmental sensor network ofclaim 7, wherein the sensors of the first environmental sensor unit andthe second environment sensor unit are adapted to measure conductivity.10. The environmental sensor network of claim 7, wherein the sensors ofthe first environmental sensor unit and the second environment sensorunit are adapted to measure resistance.
 11. The environmental sensornetwork of claim 1, wherein the first environmental sensor unit and thesecond environmental sensor unit each include a controller adapted tocause the sensor to measure the condition and to cause the transmitterto transmit the measurement.
 12. The environmental sensor network ofclaim 1, wherein the transmitters of the first environmental sensor unitand the second environmental sensor unit transmit over a wirelesschannel.
 13. The environmental sensor network of claim 1, wherein thecentral display unit further includes a screen adapted to displayinformation based on the measurement.
 14. The environmental sensornetwork of claim 1, wherein the processor is further adapted to enter a“wait” state while in the “add” mode.